1. Field of the Invention
This invention refers to radar systems capable of detecting and localizing specific targets, specifically helicopters.
2. Description of the Prior Art
In radar surveillance operations, the problem of specific identification of target type is presented. In the case of helicopters, the problem is often complicated by the fact that on the one hand they can hover and, on the other hand, their controllability permits them to hide behind a screen of foliage. Targets masked by foliage can be detected, however, by the use of relatively long wave-lengths. But the use of long wave-lengths implies poor range and angle resolution. The precision of target position measurement can be increased by well known techniques called "simultaneous beam," or "monopulse," but these techniques however do not improve resolution, that is to say the capability of the radar to separate two targets close to each other. In other words, in order for the target position measurement by a monopulse radar to be correct, there must be only one echo in the resolution cell. This resolution cell can be reduced in range by the use of pulse compression, and the target position measurement can be improved by MTI techniques and other techniques affording elimination of undesirable echoes, that is to say in this case those coming from targets other than helicopters.